Research Articles (Geography)

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  • ItemOpen Access
    Characterisation of evapotranspiration in the Orange River Basin of South Africa-Lesotho with climate and MODIS data
    (MDPI, 2023) Mahasa, Pululu S.; Xulu, Sifiso; Mbatha, Nkanyiso
    Evapotranspiration (ET) is crucial to the management of water supplies and the functioning of numerous terrestrial ecosystems. To understand and propose planning strategies for water-resource and crop management, it is critical to examine the geo-temporal patterns of ET in drought-prone areas such as the Upper Orange River Basin (UORB) in South Africa. While information on ET changes is computed from directly observed parameters, capturing it through remote sensing is inexpensive, consistent, and feasible at different space–time scales. Here, we employed the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived spectral indices within Google Earth Engine (GEE) to analyze and characterize patterns of ET over the UORB from 2003 to 2021, in association with various climatic parameters. Our results show spatially consistent ET patterns with the Vegetation Condition Index (VCI), with lower values in the west, increasing toward the eastern section of the basin, over the Lesotho highlands. We noted that the UORB faced significant variability in ET and VCI during pronounced drought episodes. The random forests (RF) model identified precipitation, temperature, Standardized Precipitation Index (SPI)-6, Palmer Drought Severity Index (PDSI), and VCI as variables of high importance for ET variability, while the wavelet analysis confirmed the coherence connectivity between these variables with periodicities ranging from eight to 32 months, suggesting a strong causal influence on ET, except for PDSI, that showed an erratic relationship. Based on the sequential Mann–Kendall test, we concluded that evapotranspiration has exhibited a statistically downward trend since 2011, which was particularly pronounced during the dry periods in 2015–2016, 2019, and 2021. Our study also confirmed the high capacity of the GEE and MODIS-derived indices in mapping consistent geo-temporal ET patterns.
  • ItemOpen Access
    Fine-scale classification of urban land use and land cover with PlanetScope imagery and machine-learning strategies in the City of Cape Town, South Africa
    (MDPI, 2022) Lefulebe, Bosiu E.; Van der Walt, Adriaan; Xulu, Sifiso
    Urban land use and land cover (LULC) change can be efficiently monitored with high-resolution satellite products for a variety of purposes, including sustainable planning. These, together with machine learning strategies, have great potential to detect even subtle changes with satisfactory accuracy. In this study, we used PlaneScope Imagery and machine learning strategies (Random Forests, Support Vector Machines, Naïve Bayes and K-Nearest Neighbour) to classify and detect LULC changes over the City of Cape Town between 2016 and 2021. Our results showed that K-Nearest Neighbour outperformed other classifiers by achieving the highest overall classification of accuracy (96.54% with 0.95 kappa), followed by Random Forests (94.8% with 0.92 kappa), Naïve Bayes (93.71% with 0.91 kappa) and Support Vector Machines classifiers with relatively low accuracy values (92.28% with 0.88 kappa). However, the performance of all classifiers was acceptable, exceeding the overall accuracy of more than 90%. Furthermore, the results of change detection from 2016 to 2021 showed that the high-resolution PlanetScope imagery could be used to track changes in LULC over a desired period accurately.
  • ItemOpen Access
    Mapping vegetation species succession in a mountainous grassland ecosystem using Landsat, ASTER MI, and Sentinel-2 data
    (Public Library of Science, 2022) Adagbasa, Efosa Gbenga; Mukwada, Geofrey
    Vegetation species succession and composition are significant factors determining the rate of ecosystem biodiversity recovery after being disturbed and subsequently vital for sustainable and effective natural resource management and biodiversity. The succession and composition of grasslands ecosystems worldwide have significantly been affected by accelerated environmental changes due to natural and anthropogenic activities. Therefore, understanding spatial data on the succession of grassland vegetation species and communities through mapping and monitoring is essential to gain knowledge on the ecosystem and other ecosystem services. This study used a random forest machine learning classifier on the Google Earth Engine platform to classify grass vegetation species with Landsat 7 ETM+ and ASTER multispectral imager (MI) data resampled with the current Sentinel-2 MSI data to map and estimate the changes in vegetation species succession. The results indicate that ASTER MI has the least accuracy of 72%, Landsat 7 ETM+ 84%, and Sentinel-2 had the highest of 87%. The result also shows that other species had replaced four dominant grass species totaling about 49 km2 throughout the study.
  • ItemOpen Access
    Burned area mapping over the Southern Cape forestry region, South Africa using sentinel data within GEE cloud platform
    (MDPI, 2021) Xulu, Sifiso; Mbatha, Nkanyiso; Peerbhay, Kabir
    Planted forests in South Africa have been affected by an increasing number of economically damaging fires over the past four decades. They constitute a major threat to the forestry industry and account for over 80% of the country’s commercial timber losses. Forest fires are more frequent and severe during the drier drought conditions that are typical in South Africa. For proper forest management, accurate detection and mapping of burned areas are required, yet the exercise is difficult to perform in the field because of time and expense. Now that ready-to-use satellite data are freely accessible in the cloud-based Google Earth Engine (GEE), in this study, we exploit the Sentinel-2-derived differenced normalized burned ratio (dNBR) to characterize burn severity areas, and also track carbon monoxide (CO) plumes using Sentinel-5 following a wildfire that broke over the southeastern coast of the Western Cape province in late October 2018. The results showed that 37.4% of the area was severely burned, and much of it occurred in forested land in the studied area. This was followed by 24.7% of the area that was burned at a moderate-high level. About 15.9% had moderate-low burned severity, whereas 21.9% was slightly burned. Random forests classifier was adopted to separate burned class from unburned and achieved an overall accuracy of over 97%. The most important variables in the classification included texture, NBR, and the NIR bands. The CO signal sharply increased during fire outbreaks and marked the intensity of black carbon over the affected area. Our study contributes to the understanding of forest fire in the dynamics over the Southern Cape forestry landscape. Furthermore, it also demonstrates the usefulness of Sentinel-5 for monitoring CO. Taken together, the Sentinel satellites and GEE offer an effective tool for mapping fires, even in data-poor countries.
  • ItemOpen Access
    A Lefebvrian analysis of public spaces in Mangaung, South Africa
    (Cogitatio Press, 2018) Nkooe, Ernestina S.
    Hoffman Square, Driehoek Neighbourhood Park and Old Regional Park are public spaces in Mangaung. Henri Lefebvre’s The Production of Space and Elements of Rhythmanalysis are explored in the analysis of these public spaces’ organised representations, representational uses and rhythmic spatial practices. This article found that: (1) public spaces in Mangaung are lived spaces that are regularly appropriated by inhabitants whose unpoliced social practices of vandalism and littering—along with the harsh regional climate—deteriorate the physical quality of the public spaces, secreting environmental incivility in the public spaces; (2) cyclical rhythms of night and day times have a practical impact on the spatial practices of each public space in spite of their design and location. For example, day-time entails high and rapid levels of public space uses while night-time diffuses these dynamics significantly; and (3) Mangaung’s spatial plans encourage the liberal uses of its public spaces however, it fails to enforce its by-laws to curb experienced physical decay of, and environmental incivility in, the public spaces. This increases the vulnerability of its public spaces to external shocks—emanating from nature and society—thus depriving the public spaces of an opportunity to be perceived as alternatives for urban regeneration and local economic revitalisation.